Organic electroluminescent materials and devices

ABSTRACT

Phosphorescent metal complexes comprising a pendant redox-active metallocene are disclosed. These complexes are useful as emitters for phosphorescent OLEDs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of the copending U.S. patent application Ser. No. 14/573,722, filed on Dec. 17, 2014.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connection with one or more of the following parties to a joint university corporation research agreement: The Regents of the University of Michigan, Princeton University, University of Southern California, and Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention relates to compounds for use as phosphorescent emitters and devices, such as organic light emitting diodes, including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

As used herein, “solution processable” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.

More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

According to an embodiment, a compound comprising a first ligand L¹ having the formula:

wherein ring A and ring B are each independently a 5-membered or 6-membered carbocyclic or heterocyclic ring;

wherein X¹, X², X³, and X⁴ are independently C or N;

wherein R^(A) and R^(B) each independently represent mono, di, tri, or tetra substitution, or no substitution;

wherein at least one of R^(A) and R^(B) has the following formula:

wherein L is a direct bond or a linker selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein R¹ represents mono, di, tri, or tetra substitution, or no substitution;

wherein R² represents mono, di, tri, tetra, or penta substitution, or no substitution;

wherein M² is selected from the group consisting of Os, Ru, and Re;

wherein R¹ and R² are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein when R^(A) and R^(B) is not Formula II, R^(A) and R^(B) are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein any two adjacent substituents are optionally joined to form a ring, which can be further substituted;

wherein the ligand L¹ is coordinated to a metal M, wherein M is selected from the group consisting of Ir, Rh, Re, Ru, Os, Pt, Au, and Cu;

wherein the metal M can be coordinated to other ligands; and

wherein the ligand L¹ is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate or hexadentate ligand.

According to another embodiment, a device comprising one or more organic light emitting devices is also provided. At least one of the one or more organic light emitting devices can include an anode, a cathode, and an organic layer, disposed between the anode and the cathode, wherein the organic layer includes the compound comprising a first ligand L¹ having the formula:

where the variables A, B, R^(A), R^(B), X¹, X², X³, and X⁴ are as defined herein, including all of the variations. The device can be a consumer product, an electronic component module, an organic light-emitting device, and/or a lighting panel.

According to yet another embodiment, a formulation comprising the compound comprising a first ligand L¹ having the formula:

where the variables A, B, R^(A), R^(B), X¹, X², X³, and X⁴ are as defined herein, including all of the variations, is provided.

The present disclosure provides a phosphorescent metal complex comprising a pendant redox-active metallocene. This metal complex system allows the optical band gap of the luminescent system to be preserved, while taking advantage of the electroactive properties of metallocene. These metal complexes are useful as emitters for phosphorescent OLEDs (PHOLEDs), especially for blue phosphorescent emitters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

FIG. 3 shows Formula I for the disclosed novel compound.

FIG. 4 shows Formula II for the substituents in Formula I.

FIG. 5 shows Formula III for the substituents in Formula I.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, a cathode 160, and a barrier layer 170. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.

More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.

Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. Pat. No. 7,431,968, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processability than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the present invention may further optionally comprise a barrier layer. One purpose of the barrier layer is to protect the electrodes and organic layers from damaging exposure to harmful species in the environment including moisture, vapor and/or gases, etc. The barrier layer may be deposited over, under or next to a substrate, an electrode, or over any other parts of a device including an edge. The barrier layer may comprise a single layer, or multiple layers. The barrier layer may be formed by various known chemical vapor deposition techniques and may include compositions having a single phase as well as compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer. The barrier layer may incorporate an inorganic or an organic compound or both. The preferred barrier layer comprises a mixture of a polymeric material and a non-polymeric material as described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos. PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporated by reference in their entireties. To be considered a “mixture”, the aforesaid polymeric and non-polymeric materials comprising the barrier layer should be deposited under the same reaction conditions and/or at the same time. The weight ratio of polymeric to non-polymeric material may be in the range of 95:5 to 5:95. The polymeric material and the non-polymeric material may be created from the same precursor material. In one example, the mixture of a polymeric material and a non-polymeric material consists essentially of polymeric silicon and inorganic silicon.

Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of electronic component modules (or units) that can be incorporated into a variety of electronic products or intermediate components. Examples of such electronic products or intermediate components include display screens, lighting devices such as discrete light source devices or lighting panels, etc. that can be utilized by the end-user product manufacturers. Such electronic component modules can optionally include the driving electronics and/or power source(s). Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of consumer products that have one or more of the electronic component modules (or units) incorporated therein. Such consumer products would include any kind of products that include one or more light source(s) and/or one or more of some type of visual displays. Some examples of such consumer products include flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads-up displays, fully or partially transparent displays, flexible displays, laser printers, telephones, cell phones, tablets, phablets, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, 3-D displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.), but could be used outside this temperature range, for example, from −40 degree C. to +80 degree C.

The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

The term “halo,” “halogen,” or “halide” as used herein includes fluorine, chlorine, bromine, and iodine.

The term “alkyl” as used herein contemplates both straight and branched chain alkyl radicals. Preferred alkyl groups are those containing from one to fifteen carbon atoms and includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, and the like. Additionally, the alkyl group may be optionally substituted.

The term “cycloalkyl” as used herein contemplates cyclic alkyl radicals. Preferred cycloalkyl groups are those containing 3 to 7 carbon atoms and includes cyclopropyl, cyclopentyl, cyclohexyl, and the like. Additionally, the cycloalkyl group may be optionally substituted.

The term “alkenyl” as used herein contemplates both straight and branched chain alkene radicals. Preferred alkenyl groups are those containing two to fifteen carbon atoms. Additionally, the alkenyl group may be optionally substituted.

The term “alkynyl” as used herein contemplates both straight and branched chain alkyne radicals. Preferred alkynyl groups are those containing two to fifteen carbon atoms. Additionally, the alkynyl group may be optionally substituted.

The terms “aralkyl” or “arylalkyl” as used herein are used interchangeably and contemplate an alkyl group that has as a substituent an aromatic group. Additionally, the aralkyl group may be optionally substituted.

The term “heterocyclic group” as used herein contemplates aromatic and non-aromatic cyclic radicals. Hetero-aromatic cyclic radicals also means heteroaryl. Preferred hetero-non-aromatic cyclic groups are those containing 3 or 7 ring atoms which includes at least one hetero atom, and includes cyclic amines such as morpholino, piperdino, pyrrolidino, and the like, and cyclic ethers, such as tetrahydrofuran, tetrahydropyran, and the like. Additionally, the heterocyclic group may be optionally substituted.

The term “aryl” or “aromatic group” as used herein contemplates single-ring groups and polycyclic ring systems. The polycyclic rings may have two or more rings in which two carbons are common to two adjoining rings (the rings are “fused”) wherein at least one of the rings is aromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls. Additionally, the aryl group may be optionally substituted.

The term “heteroaryl” as used herein contemplates single-ring hetero-aromatic groups that may include from one to three heteroatoms, for example, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine and pyrimidine, and the like. The term heteroaryl also includes polycyclic hetero-aromatic systems having two or more rings in which two atoms are common to two adjoining rings (the rings are “fused”) wherein at least one of the rings is a heteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls. Additionally, the heteroaryl group may be optionally substituted.

The alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, heterocyclic group, aryl, and heteroaryl may be optionally substituted with one or more substituents selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

As used herein, “substituted” indicates that a substituent other than H is bonded to the relevant position, such as carbon. Thus, for example, where R¹ is mono-substituted, then one R¹ must be other than H. Similarly, where R¹ is di-substituted, then two of R¹ must be other than H. Similarly, where R¹ is unsubstituted, R¹ is hydrogen for all available positions.

The “aza” designation in the fragments described herein, i.e. aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more of the C—H groups in the respective fragment can be replaced by a nitrogen atom, for example, and without any limitation, azatriphenylene encompasses both dibenzo[f,h]quinoxaline and dibenzo[f,h]quinoline. One of ordinary skill in the art can readily envision other nitrogen analogs of the aza-derivatives described above, and all such analogs are intended to be encompassed by the terms as set forth herein.

It is to be understood that when a molecular fragment is described as being a substituent or otherwise attached to another moiety, its name may be written as if it were a fragment (e.g. phenyl, phenylene, naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g. benzene, naphthalene, dibenzofuran). As used herein, these different ways of designating a substituent or attached fragment are considered to be equivalent.

The present disclosure provides a novel phosphorescent dopant system with the general structure represented by Formula I described below. Inventors believe that the disclosed phosphorescent dopants have beneficially small band gap while maintaining the triplet energy.

The present disclosure provides a novel compound comprising a first ligand L¹ having the Formula:

wherein ring A and ring B are each independently a 5-membered or 6-membered carbocyclic or heterocyclic ring;

wherein X¹, X², X³, and X⁴ are independently C or N;

wherein R^(A) and R^(B) each independently represent mono, di, tri, or tetra substitution, or no substitution;

wherein at least one of R^(A) and R^(B) has a structure according to the following formula:

wherein L is a direct bond or a linker selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein R¹ represents mono, di, tri, or tetra substitution, or no substitution;

wherein R² represents mono, di, tri, tetra, or penta substitution, or no substitution;

wherein M² is selected from the group consisting of Os, Ru, and Re;

wherein R¹ and R² are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein when R^(A) and R^(B) is not Formula II, R^(A) and R^(B) are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein any two adjacent substituents are optionally joined to form a ring, which can be further substituted;

wherein the ligand L¹ is coordinated to a metal M;

wherein the metal M can be coordinated to other ligands; and

wherein the ligand L¹ is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate or hexadentate ligand.

In one embodiment of the compound, M is selected from the group consisting of Ir, Rh, Re, Ru, Os, Pt, Au, and Cu. In some embodiments of the compound, M is Ir or Pt.

In the compound, ring A and ring B are each independently a 5-membered or 6-membered aromatic or heteroaromatic ring.

In another embodiment of the compound, at least one of R^(A) and R^(B) has a structure according to the following formula:

and

wherein R⁵ and R⁶ are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment of the compound, the ligand L¹ is selected from the group consisting of:

wherein R¹, R², R⁵, and R⁶ are as defined above;

wherein R³ and R⁴ each independently represent mono, di, tri, or tetra substitution, or no substitution;

wherein R⁷ represents mono, di or tri substitution, or no substitution; and

wherein R³, R⁴, R⁵, R⁶, and R⁷ are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

The compound can be homoleptic or heteroleptic. In other embodiments, the compound is neutral.

In some embodiments of the compound, the ligand L¹ is selected from the group consisting of:

In another embodiment of the compound, the compound has the formula of M(L¹)_(x)(L²)_(y)(L³)_(z);

wherein L² is a second ligand, and L³ is a third ligand, and L² and L³ can be the same or different;

wherein x is 1, 2, or 3;

wherein y is 0, 1, or 2;

wherein z is 0, 1, or 2;

wherein x+y+z is the oxidation state of the metal M;

wherein the second ligand L² and the third ligand L³ are independently selected from the group consisting of:

wherein R_(a), R_(b), R_(c), and R_(d) may represent mono, di, tri, or tetra substitution, or no substitution;

wherein R_(a), R_(b), R_(c), and R_(d) are independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and

wherein two adjacent substituents of R_(a), R_(b), R_(c), and R_(d) are optionally joined to form a fused ring or form a multidentate ligand.

In one embodiment of the compound having the formula of M(L¹)_(x)(L²)_(y)(L³)₇, the compound has the formula of Ir(L¹)(L²)₂.

In another embodiment of the compound having the formula of M(L¹)_(x)(L²)_(y)(L³)_(z), the compound has the formula of Pt(L¹)₂ or Pt(L¹)(L²). In some embodiments, L¹ can be connected to the other L¹ or L² to form a tetradentate ligand.

In another embodiment of the compound comprising a first ligand L¹ having a structure according to Formula I:

described above, the compound is selected from the group consisting of:

According to another aspect of the present disclosure, a device comprising one or more organic light emitting devices is disclosed. At least one of the one or more organic light emitting devices comprise: an anode; a cathode; and

an organic layer, disposed between the anode and the cathode, the organic layer comprising a compound comprising a first ligand L¹ of Formula I:

wherein ring A and ring B are each independently a 5-membered or 6-membered carbocyclic or heterocyclic ring;

wherein X¹, X², X³, and X⁴ are independently C or N;

wherein R^(A) and R^(B) each independently represent mono, di, tri, or tetra substitution, or no substitution;

wherein at least one of R^(A) and R^(B) has a structure according to the following formula:

wherein L is a direct bond or a linker selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein R¹ represents mono, di, tri, or tetra substitution, or no substitution;

wherein R² represents mono, di, tri, tetra, or penta substitution, or no substitution;

wherein M² is selected from the group consisting of Os, Ru, and Re;

wherein R¹ and R² are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein when R^(A) and R^(B) is not Formula II, R^(A) and R^(B) are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein any two adjacent substituents are optionally joined to form a ring, which can be further substituted;

wherein the ligand L¹ is coordinated to a metal M;

wherein the metal M can be coordinated to other ligands; and

wherein the ligand L¹ is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate or hexadentate ligand.

The device can be one or more of a consumer product, an electronic component module, an organic light-emitting device and a lighting panel. The organic layer can be an emissive layer and the compound can be an emissive dopant in some embodiments, while the compound can be a non-emissive dopant in other embodiments.

The organic layer can also include a host. In some embodiments, the host can include a metal complex. The host can be a triphenylene containing benzo-fused thiophene or benzo-fused furan. Any substituent in the host can be an unfused substituent independently selected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C≡C—C_(n)H_(2n+1), Ar₁, Ar₁-Ar₂, and C_(n)H_(2n)—Ar₁, or no substitution. In the preceding substituents n can range from 1 to 10; and Ar₁ and Ar₂ can be independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof.

In another embodiment, the host can be a compound comprising at least one chemical group selected from the group consisting of triphenylene, carbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene, azatriphenylene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene. In some embodiments of the device, the host can include a metal complex.

In yet another embodiment, the host can be a specific compound selected from the group consisting of:

and combinations thereof.

According to another aspect of the present disclosure, a formulation comprising the compound comprising a first ligand L¹ of Formula I:

wherein ring A and ring B are each independently a 5-membered or 6-membered carbocyclic or heterocyclic ring;

wherein X¹, X², X³, and X⁴ are independently C or N;

wherein R^(A) and R^(B) each independently represent mono, di, tri, or tetra substitution, or no substitution;

wherein at least one of R^(A) and R^(B) has a structure according to the following formula:

wherein L is a direct bond or a linker selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein R¹ represents mono, di, tri, or tetra substitution, or no substitution;

wherein R² represents mono, di, tri, tetra, or penta substitution, or no substitution;

wherein M² is selected from the group consisting of Os, Ru, and Re;

wherein R¹ and R² are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein when R^(A) and R^(B) is not Formula II, R^(A) and R^(B) are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein any two adjacent substituents are optionally joined to form a ring, which can be further substituted;

wherein the ligand L¹ is coordinated to a metal M;

wherein the metal M can be coordinated to other ligands; and

wherein the ligand L¹ is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate or hexadentate ligand is disclosed. The formulation can include one or more components selected from the group consisting of a solvent, a host, a hole injection material, hole transport material, and an electron transport layer material, disclosed herein.

In some embodiments, the compound can be an emissive dopant in an OLED. In some embodiments, the compound can produce emissions via phosphorescence, fluorescence, thermally activated delayed fluorescence, i.e., TADF (also referred to as E-type delayed fluorescence), triplet-triplet annihilation, or combinations of these processes.

Combination with other Materials

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the present invention is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but are not limited to: a phthalocyanine or porphyrin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and silane derivatives; a metal oxide derivative, such as MoO_(x); a p-type semiconducting organic compound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and a cross-linkable compound.

Examples of aromatic amine derivatives used in HIL or HTL include, but are not limited to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting of aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene; the group consisting of aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and the group consisting of 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each Ar is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the group consisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH) or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but are not limited to the following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40; (Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independently selected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative. In another aspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met is selected from Ir, Pt, Os, and Zn. In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant. While the Table below categorizes host materials as preferred for devices that emit various colors, any host material may be used with any dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have the following general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴ are independently selected from C, N, O, P, and S; L¹⁰¹ is an another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, Met is selected from Ir and Pt. In a further aspect, (Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the group consisting of aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene; the group consisting of aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and the group consisting of 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each group is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, the host compound contains at least one of the following groups in the molecule:

wherein R¹⁰¹ to R¹⁰⁷ is independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above. k is an integer from 0 to 20 or 1 to 20; k′″ is an integer from 0 to 20. X¹⁰¹ to X¹⁰⁸ is selected from C (including CH) or N. Z¹⁰¹ and Z¹⁰² is selected from NR¹⁰¹, O, or S. HBL:

A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED.

In one aspect, compound used in HBL contains the same molecule or the same functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of the following groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ is an integer from 1 to 3. ETL:

Electron transport layer (ETL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic compounds may be used as long as they are typically used to transport electrons.

In one aspect, compound used in ETL contains at least one of the following groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above. Ar¹ to Ar³ has the similar definition as Ar's mentioned above. k is an integer from 1 to 20. X¹⁰¹ to X¹⁰⁸ is selected from C (including CH) or N.

In another aspect, the metal complexes used in ETL include, but are not limited to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L¹⁰¹ is another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated. Thus, any specifically listed substituent, such as, without limitation, methyl, phenyl, pyridyl, etc. encompasses undeuterated, partially deuterated, and fully deuterated versions thereof. Similarly, classes of substituents such as, without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc. also encompass undeuterated, partially deuterated, and fully deuterated versions thereof.

In addition to and/or in combination with the materials disclosed herein, many hole injection materials, hole transporting materials, host materials, dopant materials, exciton/hole blocking layer materials, electron transporting and electron injecting materials may be used in an OLED. Non-limiting examples of the materials that may be used in an OLED in combination with materials disclosed herein are listed in Table A below. Table A lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials.

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Inventors believe that the disclosed phosphorescent dopants having the general structure represented by Formula I described herein have beneficially small electrochemical band gap while maintaining the triplet energy. The inventors have determined that the linkage of a pendant redox-active ligand to a conjugated system would allow the electrochemical gap of the whole molecule to be modulated without altering the optical property. Table 1 shows the calculated HOMO, LUMO, and electrochemical gap for inventive compounds Compound 8 and Compound 1 and the comparative compounds Compound A and Compound B. Compound A and Compound 8 have the same triplet energy, but Compound 8 has a shallower HOMO than Compound A because of the pendant osmocene group on Compound 8. As a result, Compound 8 has a smaller electrochemical gap than Compound A (3.30 eV vs. 3.65 eV). Likewise, Compound 1 has the same triplet energy as Compound B, but Compound 1 has a smaller electrochemical gap than Compound B because of the pendant osmocene group on Compound 1. Phosphorescent dopants, such as the novel compounds represented by compounds 8 and 1 with a smaller electrochemical gap is highly desirable for OLED application.

Smaller electrochemical gap is believed to provide better stability toward charges. In addition, shallower HOMO and deeper LUMO energy levels can provide charge trapping sites and confinement of triplet energy on the emitter, which can result in high device efficiency. For most of the phosphorescent emitters, the electrochemical gap is correlated to the optical bandgap. Emitters having higher optical bandgap usually have larger electrochemical bandgap. This is one of the reasons that blue phosphorescent devices have short device lifetime. The current invention provides a way to maintain the optical bandgap while shrinking the electrochemical gap. As a result, the current invention provides more stable phosphorescent emitters.

TABLE 1 Calculated HOMO/LUMO levels HOMO (eV) LUMO (eV) Gap (eV) T1

−5.41 −1.76 −3.65 489 nm Compound A

−5.01 −1.71 −3.30 489 nm Compound 8

−5.85 −2.07 −3.79 472 nm Compound B

−5.54 −1.94 −3.60 471 nm Compound 1

SYNTHESIS Synthesis of Compound 1 Synthesis of 2-(4-chloro-2,6-dimethylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

A 500 ml round bottom flask was charged with 1-bromo-4-isopropylbenzene (13.5 g, 67.8 mmol) and 200 mL of THF. N-butyllithium in hexane (2.5M, 32.5 ml, 81 mmol) was added dropwise to the reaction mixture at −78° C. The reaction mixture was then stirred at −78° C. for 45 minutes. 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (20.19 g, 108 mmol) in 20 mL of THF was then added to the reaction mixture dropwise at −78° C. The reaction mixture was stirred and allowed to slowly warm to room temperature (20-25° C.). The reaction mixture was quenched with aqueous ammonium chloride then was extracted 2×300 mL ethyl acetate. These extracts were combined and were washed with aqueous LiCl. The extracts were then combined and passed through a 400 g silica gel column using 20% DCM/heptanes as the eluent and yielded the desired compound, 2-(4-chloro-2,6-dimethylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, (14.3 g, 93%).

Synthesis of 5-bromo-2-(2,4-difluorophenyl)pyridine

One 1.0 L round bottom flask was charged with 2,5-dibromopyridine (10.45 g, 44.1 mmol); (2,4-difluorophenyl) boronic acid (7.66 g, 48.5 mmol); potassium carbonate (12.19 g, 88 mmole); diacetoxypalladium (0.495 g, 2.206 mmol); triphenylphosphine (1.157 g, 4.41 mmol); and acetonitrile (348 ml) and MeOH (174 ml). The reaction mixture was heated to 40° C. for 40 hours. The reaction mixture was diluted with deionized water and extracted with ethyl acetate. The organic portion was combined and subjected to column chromatography (SiO₂ gel, 10% EtOAc in heptane) to yield the desired compound, 5-bromo-2-(2,4-difluorophenyl)pyridine (10 g; 84%).

Synthesis of 5-(4-chloro-2,6-dimethylphenyl)-2-(2,4-difluorophenyl)pyridine

One 100 mL round-bottomed flask was charged with 5-bromo-2-(2,4-difluorophenyl)pyridine (0.5 g, 1.851 mmol), 2-(4-chloro-2,6-dimethylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.730 g, 2.74 mmol), dicyclohexyl(2′,4′,6′-triisopropyl-[1,1′-biphenyl]-3-yl)phosphine (0.021 g, 0.044 mmol), diacetoxypalladium (8.31 mg, 0.037 mmol), and butanol (Volume: 6 ml) to give a yellow suspension. The reaction mixture was then stirred for 15 minutes at room temperature. Lithium hydroxide (0.075 g, 3.15 mmol) was added into reaction mixture and then heated to 80° C. for 1 hour. The reaction mixture was then diluted with deionized water and extracted by ethyl acetate. The organic portion was combined and subjected to column chromatography (SiO₂ gel, 5% EtOAc in heptane) to yield the desired compound, 5-(4-chloro-2,6-dimethylphenyl)-2-(2,4-difluorophenyl)pyridine (0.525 g, 86%).

Synthesis of 2-(2,4-difluorophenyl)-5-(2,6-dimethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine

One 250 mL round-bottomed flask was charged with Pd2DBA3 (0.083 mmole, 0.076 g), 5-(4-chloro-2,6-dimethylphenyl)-2-(2,4-difluorophenyl)pyridine (1.362 g, 4.13 mmol), 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi(1,3,2-dioxaborolane) (1.363 g, 5.37 mmol), potassium acetate (1.257 g, 12.80 mmol), tricyclohexylphosphine (0.093 g, 0.330 mmol), and Dioxane (20 ml) to give a yellow solution. The reaction mixture was refluxed for 12 hours. Then the reaction mixture was diluted with deionized water and extracted by ethyl acetate. The organic portion was combined and subjected to column chromatography (SiO₂ gel, 20% EtOAc in heptane) to yield the desired compound, 2-(2,4-difluorophenyl)-5-(2,6-dimethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine (1.5 g, 86%).

Synthesis of the Ligand for Compound B1

One 100 ml round-bottomed flask was charged with bromoosmocence (3.17 g, 7.94 mmole); 2-(2,4-difluorophenyl)-5-(2,6-dimethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine (3.68 g, 8.73 mmol), Xphos Pd G3 (a.k.a. (2-Dicyclohexylphosphino-2′,4′,6′-triisopropyl-1,1′-biphenyl)[2-(2′-amino-1,1′-biphenyl)]palladium(II) methanesulfonate, XPhos-G3-Palladacycle) (0.53 g, 0.63 mmole), dicyclohexyl(2′,4′,6′-triisopropyl-[1,1′-biphenyl]-2-yl)phosphine (0.303 g, 0.635 mmol), dioxane (25 ml) and 0.5M of K₃PO₄ aqueous solution (25 ml) to give a yellow suspension. The reaction mixture was heated to 40° C. for 8 hours. The reaction mixture was then diluted with deionized water and extracted by EtOAc. The organic portion was combined and subjected to column chromatography (5% EtOAc in heptane) to yield the desired ligand (1.17 g, 24%).

Synthesis of Iridium Dichloro Bridge Dimer Synthesis of Dichloro Bridge Dimer

One 100 mL round-bottomed flask was charged with 2-(2,4-difluorophenyl)pyridine (5 g, 26.2 mmol), iridium chloride (4.61 g, 13.08 mmol), 2-ethoxyethanol (40 ml) and deionized water (10.00 ml) to give a tan colored suspension. The reaction mixture was heated to reflux for 18 hours. The reaction mixture was filtered and the precipitate was collected and washed with methanol to yield dichloro bridge dimer (6.48 g; 81%)

Synthesis of Iridium Solvento Complexes

One 1000 ml round-bottomed flask was charged with the dichloro bridge dimer (6.45 g, 5.31 mmole), silver trifluoromethanesulfonate (2.73 g, 10.62 mmole), dichloromethane (200 ml) and MeOH (200 ml) to give a yellow suspension. The reaction mixture was then stirred at room temperature until the reaction mixture reached room temperature. The reaction mixture was filtered and the filtrate was concentrated to dryness to yield iridium solvento complexes (8.35 g, 100%).

Synthesis of Compound 1

One 100 ml round-bottomed flask was charged with iridium solvento complexes (2.247 g, 2.86 mmole), ligand (1.17 g, 1.906 mmole), 2-ethoxyethanol (50 ml), and DMF (50.0 ml) to give a yellow suspension. The reaction mixture was then heated to 150° C. for 24 hours. The solvent was evaporated to dryness and the residue was subjected to a column chromatography (SiO₂, 40% DCM in heptane) to yield the mer isomer (1.78 g). The Mer isomer (1.78 g) was dissolved in DMSO (450 ml) and acetonitrile (1000 ml) and then subjected to photolysis for 16 hours. After photolysis is completed, the solvent was evaporated to dryness. The residue was subjected to a column chromatography (SiO₂ gel, 40% DCM in heptane) to yield Compound 1. (0.934 g, 41%).

Synthesis of Compound 36 Detailed Synthesis Synthesis of 4-bromo-2,6-diisopropylaniline

A three neck round bottom flask was charged with 2,6-diisopropylaniline (22.96 g, 130 mmol) and DMF (Volume: 250 ml). A solution of 1-bromopyrrolidine-2,5-dione (23.05 g, 130 mmol) in 100 ml DMF was added into reaction mixture drop wise at 0° C. After addition was over; reaction mixture was stirred for 2 days at room temperature. The reaction mixture was poured into 500 ml deionized water and extracted with 3×150 ml ether. The combined extracts were washed with 150 ml deionized water, 150 ml 10% lithium chloride, dried over MgSO₄ and evaporated to dryness. The residue was purified by vacuum distillation to yield 4-bromo-2,6-diisopropylaniline (32.3 g; 97%).

Synthesis of N-(4-bromo-2,6-diisopropylphenyl)-3-methoxybenzimidamide

One 2 L 3-neck flask was charged with 4-bromo-2,6-diisopropylaniline (19 g, 74.2 mmol) and toluene (200 ml). Trimethylaluminum (2M solution in toluene, 25 ml) was added dropwise into the reaction mixture at °0 C. After the addition was over, the ice bath was removed and reaction mixture was allowed to stir at room temperature (20-25° C.) for 3 hours. 3-methoxybenzonitrile (9.88 g, 74.2 mmol) in toluene (300 ml) was then added into reaction mixture. The reaction mixture was allowed to heated to 80° C. for 17 hours. The reaction mixture was poured slowly into a slurry of 200 gm of celite in 900 ml of a 2:1 mixture of DCM in methanol. The reaction mixture was then filtered and filtrate was evaporated to dryness, the residue was re-suspend with heptane and filtered to yield N-(4-bromo-2,6-diisopropylphenyl)-3-methoxybenzimidamide (19.73 g, 68%).

Synthesis of 1-(4-bromo-2,6-diisopropylphenyl)-2-(3-methoxyphenyl)-1H-imidazole

A 500 ml round bottom flask was charged with N-(4-bromo-2,6-diisopropylphenyl)-3-methoxybenzimidamide (19.73 g, 50.7 mmol), 2-chloroacetaldehyde (12.83 ml, 101 mmol), sodium bicarbonate (12.77 g, 152 mmole) and 2-Propanol (300 ml). The reaction was allowed to reflux for 16 hours. The reaction mixture was diluted with deionized water and extracted with ethyl acetate, the organic portion was combined and subjected to a column chromatography (SiO₂ gel; 20% THF in heptane) to yield the desired product (16.47 g, 79%).

Synthesis of 3-(1-(4-bromo-2,6-diisopropylphenyl)-1H-imidazol-2-yl)phenol

A 250 mL round-bottomed flask was charged with 3-(2,6-diisobutylphenyl)-11-methoxyimidazo[1,2-f]phenanthridine (2.01 g, 4.60 mmol) and CH₂Cl₂ (Volume: 100 ml), tribromoborane (tribromoborane (120 ml of 1M solutiontribromoborane (120 ml, 120 mmol) was added dropwise at −78° C. After the addition was over, the dry-ice bath was removed and reaction mixture was stirred until the reaction mixture reached room temperature (20-25° C.). Reaction mixture was diluted with cold deionized water and neutralized by ammonium hydroxide, extracted by dichloromethane. The organic portion was combined and subjected to a column chromatography (SiO₂ gel, 2% to 5% MeOH in dichloromethane) to yield the desired product, 3-(1-(4-bromo-2,6-diisopropylphenyl)-1H-imidazol-2-yl)phenol (15 g, 94%).

Synthesis of 4′-Bromo-2-nitro-1,1′-biphenyl

1-Iodo-2-nitrobenzene (28.2 g, 113 mmol), (4-bromophenyl)boronic acid (25 g, 124 mmol), Pd(Ph₃P)₄ (1.3 g, 1.1 mmol), potassium carbonate (46.9 g, 340 mmol), DME (300 mL) and water (200 mL) were added to a flask and degassed with nitrogen for 20 minutes. The reaction mixture was heated to reflux for 16 hours. The reaction mixture was then cooled to room temperature (20-25° C.) and 200 mL of EtOAc and 200 mL of deionized water were added into reaction mixture. After separating the layers, the aqueous layer was washed twice with EtOAc and the combined organics was washed twice with deionized water. The combined organic portion was dried over sodium sulfate, filtered and evaporated to dryness to give 34.3 g of an amber oil. The oil was then subjected to a column chromatography (SiO₂ gel, 9/1 hexane/EtOAc) to yield 23.7 g (75%) of 4′-bromo-2-nitro-1,1′-biphenyl. The product was confirmed by GC/MS and NMR.

Synthesis of 2-Bromo-9H-carbazole

A round bottom flask was charged with 4′-bromo-2-nitro-1,1′-biphenyl (14.5 g, 52.1 mmol), triethyl phosphite (50 g, 301 mmol) and heated to reflux under nitrogen overnight. The reaction mixture was allowed to cool to room temperature (20-25° C.) and 60 mL of 6 N HCl was added dropwise. The reaction mixture was then heated to 80° C. for 3 hours. The reaction mixture was then cooled to 5° C. and neutralized with 50% NaOH, diluted with deionized water and extracted with 3×150 mL EtOAc. The combined extracts were washed with 150 mL deionized water and 150 mL brine, dried over MgSO₄ and evaporated to dryness. The lower boiling impurities were removed by Kugelrohr distillation and the residue was subjected to a column chromatography (SiO₂ gel, 9/1 hexane/EtOAc) to yield 8.4 g (65%) of 2-Bromo-9H-carbazole as an off-white solid. The product was confirmed by GC/MS and NMR.

Synthesis of 2-Bromo-9-(pyridin-2-yl)-9H-carbazole

A 100 mL 3-neck flask was charged with copper iodide (0.057 g, 0.301 mmol), 2-bromo-9H-carbazole (7.4 g, 30.1 mmol), 2-iodopyridine (12.3 g, 60.1 mmol), potassium phosphate (12.8 g, 60.1 mmol), (1R,4R)-cyclohexane-1,4-diamine (0.343 g, 3.0 mmol), and dioxane (25 mL) and the reaction mixture was heated at 65° C. for 16 hours. The reaction mixture was then poured into deionized water and extracted with dichloromethane The organic layers were combined and subjected to a column chromatography (neutral Al₂O₃, 99/1 hexane/EtOAc) to yield 4.2 g (43%) of 2-bromo-9-(pyridin-2-yl)-9H-carbazole as a white solid. The product was confirmed by GC/MS and NMR.

Synthesis of 2-iodo-9-(pyridin-2-yl)-9H-carbazole

A 100 ml three neck round bottom flask was charged with 2-bromo-9-(pyridin-2-yl)-9H-carbazole (10.15 g, 31.4 mmol), copper(I) iodide (1.196 g, 6.28 mmol), N1,N2-dimethylcyclohexane-1,2-diamine (1.981 ml, 12.56 mmol), sodium iodide (18.83 g, 126 mmol), and Dioxane (60 ml.). The reaction mixture was then heated to reflux for 18 hours. The reaction mixture was diluted with deionized water and extracted with ethyl acetate. The organic portion was combined and subjected to column chromatography (SiO2, 50% DCM in heptane) to yield 2-iodo-9-(pyridin-2-yl)-9H-carbazole (9.66 g, 83%).

Synthesis of 2-(3-(1-(4-bromo-2,6-diisopropylphenyl)-1H-imidazol-2-yl)phenoxy)-9-(pyridin-2-yl)-9H-carbazole

A 500 ml three neck flask was charged with 2-iodo-9-(pyridin-2-yl)-9H-carbazole (6.59 g, 17.80 mmol), copper(I) iodide (0.323 g, 1.695 mmol), picolinic acid (0.417 g, 3.39 mmol), K₃PO₄ (7.20 g, 33.9 mmol), and DMSO (160 ml). The reaction mixture was heated to 90° C. for 90 hours. The reaction mixture was diluted with 10% LiCl aqueous solution and extracted with ethyl acetate. The organic layer was concentrated and subjected to a column chromatography (SiO₂ gel, 30% EtOAc in heptane) to yield the desired product, 2-(3-(1-(4-bromo-2,6-diisopropylphenyl)-1H-imidazol-2-yl)phenoxy)-9-(pyridin-2-yl)-9H-carbazole (7.11 g, 65%).

Synthesis of 2-(3-(1-(2,6-diisopropyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1H-imidazol-2-yl)phenoxy)-9-(pyridin-2-yl)-9H-carbazole

A three neck round bottom flask was charged with 2-(3-(1-(4-bromo-2,6-diisopropylphenyl)-1H-imidazol-2-yl)phenoxy)-9-(pyridin-2-yl)-9H-carbazole (7.11 g, 11.08 mmol), 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi(1,3,2-dioxaborolane) (8.44 g, 33.2 mmol), Pd₂DBA₃ (0.203 g, 0.222 mmol), dicyclohexyl(2′,4′,6′-triisopropyl-[1,1′-biphenyl]-2-yl)phosphine (0.423 g, 0.887 mmol), potassium acetate (3.26 g, 33.2 mmol), and Dioxane (150 ml). The reaction mixture was allowed to reflux for 16 hours. The reaction mixture was diluted with 10% LiCl aqueous solution and extracted by Ethyl acetate. The organic portion was combined and subjected to a column chromatography (SiO₂ gel, 30% EtOAc in heptane;) to yield (1)(6.90 g) (90%) of 2-(3-(1-(2,6-diisopropyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1H-imidazol-2-yl)phenoxy)-9-(pyridin-2-yl)-9H-carbazole.

Synthesis of Compound 36 Synthesis of Ligand for Compound C1

A 5 ml round bottom flask was charged with Bromoosmocence (50 mg, 0.125 mmole), 2-(3-(1-(2,6-diisopropyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1H-imidazol-2-yl)phenoxy)-9-(pyridin-2-yl)-9H-carbazole (95 mg, 0.138 mmol), diacetoxypalladium (1.124 mg, 5.01 μmol), dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-3-yl), phosphine (4.11 mg, 10.02 μmol), K₃PO₄ (53.2 mg; 0.25 mmole), and DMF (1.5 ml). The reaction mixture was heated to 120° C. for 16 hours. The reaction mixture was diluted with deionized water and extracted by ethyl acetate. The organic portion was combined and subjected to a column chromatography (SiO₂ gel; 30% EtOAc in heptane) to yield the Ligand for Compound C1 (78 mg, 70%).

Synthesis of Compound 36

One 10 ml tube was charged with the Ligand for Compound 36 (0.385 g, 0.437 mmol); K₂PtCl₄ (0.181 g, 0.437 mmol); aceteic acid (1.98 ml) and deionized water (0.2 ml). The reaction mixture was subjected to microwave with temperature setting of 160° C. (200 W) for 1 hour and 19 minutes. The suspension was filtered to yield crude product. The crude product was further purified by a column chromatography (SiO₂ gel, 40% dichloromethane in heptane) to yield Compound 36 (0.4 g, 85%).

Table 2 below lists the HOMO/LUMO levels of another novel phosphorescent dopant Compound 36 according to the present disclosure and a comparative compound Compound C that were evaluated by Cyclic Voltammetry. Compound C and 36 have the same triplet energy but Compound 36 has a shallower HOMO than Compound C because of the pendant osmocene group on Compound 36. As a result, Compound 36 has a smaller electrochemical gap than Compound C.

TABLE 2 Comparison of HOMO/LUMO levels evaluated via Cyclic Voltammetry data Oxidation Reduction potential Potential Gap (eV) T1

0.46 V −2.56 V 3.02 470 nm Compound C

0.35 V −2.45 V 2.80 470 nm Compound 36

Condition for electrochemistry: Anhydrous DMF was used as the solvent under an inert atmosphere, and 0.1M tetra(n-butyl)ammonium hexafluorophosphate was used as the supporting electrolyte. A glassy carbon rod was used as the working electrode, a platinum wire was used as the counter electrode, and a silver wire was used as a pseudo-reference electrode. The redox potentials are based on values measured from differential pulsed voltammetry and are reported relative to a ferrocence/ferrocenium (Cp₂Fe/Cp₂Fe⁺) redox couple that was used as an internal reference.

It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting. 

What is claimed is:
 1. A compound comprising a first ligand L¹ having the Formula:

wherein ring A is an imidazole or its derived carbene, and ring B is a phenyl; wherein X¹ and X² are independently N or C; wherein X³ and X⁴ are C; wherein R^(A) and R^(B) each independently represent mono, di, tri, or tetra substitution, or no substitution; wherein at least one of R^(A) and R^(B) is present and has a structure according to the following formula:

wherein L is a direct bond or a linker selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein R¹ represents mono, di, tri, or tetra substitution, or no substitution; wherein R² represents mono, di, tri, tetra, or penta substitution, or no substitution; wherein M² is selected from the group consisting of Os, Ru, and Re; wherein R¹ and R² are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein when R^(A) and R^(B) is not Formula II, R^(A) and R^(B) are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein any two adjacent substituents are optionally joined to form a ring, which can be further substituted; wherein the ligand L¹ is coordinated to Ir; wherein the Ir can be coordinated to other ligands; and wherein the ligand L¹ is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate or hexadentate ligand.
 2. The compound of claim 1, wherein at least one of R^(A) and R^(B) has a structure according to the following formula:

and wherein R⁵ and R⁶ are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 3. The compound of claim 1, wherein the ligand L¹ is selected from the group consisting of:

and wherein R³ and R⁴ each independently represent mono, di, tri, or tetra substitution, or no substitution; wherein R⁷ represents mono, di or tri substitution, or no substitution; and wherein R³, R⁴, R⁵, R⁶, and R⁷ are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 4. The compound of claim 1, wherein the compound is homoleptic.
 5. The compound of claim 1, wherein the compound is heteroleptic.
 6. The compound of claim 1, wherein the compound is neutral.
 7. The compound of claim 1, wherein the ligand L¹ is selected from the group consisting of:


8. The compound of claim 1, wherein the compound has the formula of M(L¹)_(x)(L²)_(y)(L³)_(z); wherein L² is a second ligand, and L³ is a third ligand, and L² and L³ can be the same or different; wherein x is 1, 2, or 3; wherein y is 0, 1, or 2; wherein z is 0, 1, or 2; wherein x+y+z is the oxidation state of the metal M; wherein the second ligand L² and the third ligand L³ are independently selected from the group consisting of:

wherein R_(a), R_(b), R_(c), and R_(d) may represent mono, di, tri, or tetra substitution, or no substitution; wherein R_(a), R_(b), R_(c), and R_(d) are independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein two adjacent substituents of R_(a), R_(b), R_(c), and R_(d) are optionally joined to form a fused ring or form a multidentate ligand.
 9. The compound of claim 8, wherein the compound has the formula of Ir(L¹)(L²)₂.
 10. The compound of claim 1, wherein the compound is selected from the group consisting of:


11. A device comprising one or more organic light emitting devices, at least one of the one or more organic light emitting devices comprising: an anode; a cathode; and an organic layer, disposed between the anode and the cathode, the organic layer comprising a compound comprising a first ligand L¹ of Formula I:

wherein ring A is an imidazole or its derived carbene, and ring B is a phenyl; wherein X¹ and X² are independently N or C, wherein X³ and X⁴ are C; wherein R^(A) and R^(B) each independently represent mono, di, tri, or tetra substitution, or no substitution; wherein at least one of R^(A) and R^(B) is present and has a structure according to the following formula:

wherein L is a direct bond or a linker selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein R¹ represents mono, di, tri, or tetra substitution, or no substitution; wherein R² represents mono, di, tri, tetra, or penta substitution, or no substitution; wherein M² is selected from the group consisting of Os, Ru, and Re; wherein R¹ and R² are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein when R^(A) and R^(B) is not Formula II, R^(A) and R^(B) are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein any two adjacent substituents are optionally joined to form a ring, which can be further substituted; wherein the ligand L¹ is coordinated to Ir; wherein the Ir can be coordinated to other ligands; and wherein the ligand L¹ is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate or hexadentate ligand.
 12. The device of claim 11, wherein the device is selected from the group consisting of a consumer product, an electronic component module, an organic light-emitting device, and a lighting panel.
 13. The device of claim 11, wherein the organic layer is an emissive layer and the compound is an emissive dopant or a non-emissive dopant.
 14. The device of claim 11, wherein the organic layer further comprises a host comprising at least one chemical group selected from the group consisting of carbazole, triphenylene, aza-triphenylene, dibenzothiophene, dibenzofuran, dibenzoselenophene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene.
 15. The device of claim 11, wherein the organic layer further comprises a host selected from the group consisting of:

and combinations thereof.
 16. A formulation comprising the compound of claim
 1. 17. The compound of claim 1, wherein ring A is an imidazole.
 18. The device of claim 11, wherein ring A is an imidazole.
 19. The compound of claim 1, wherein ring A is an imidazole derived carbene.
 20. The device of claim 11, wherein ring A is an imidazole derived carbene. 